For two years I have heard about the terrifying star eater bug ("feature") in the Sony A7- series. Following a discussion in the Astrobin forum, I performed some experiments on my own A6000 to clarify if this model is also affected.
The "feature" shows itself when going from the internally available exposure times (up to 30s) to bulb mode. Once you use bulb, some special noise correction kicks in (spatial filtering) which removes everything that looks like hot pixels. Well, and is your alignment is good, many of the stars are only a few pixels small! This bug drives people crazy, especially the ones that want to use a A7s for Astrophotography.
I myself have always wondered why my milky way wide field photos with a 12mm lens and the A6000 looked so ugly compared to my older NEX-5N from Sony.
This test now confirms that the A6000 suffers from the same noise correction in bulb mode. To compare the different modes, I took photos with 30s by using the camera exposure and then I took again 30s photos by using the bulb mode.
Take a look, it is fucked up. Damn, Sony!!
All images were taken at ISO400, f/4, right next after each other. 10 images for each timing and stacked (except version C which shows a single frame comparison)
Edit 1: There are also many other strange things: The background changes color a littlebit between the two modes. Also, many of the brighter stars change color. Furthermore, the background noise looks completely different. I am afraid that dark frames won't help here, if this noise is not original anymore but processed in some way.
Edit 2: Further reads:
http://www.cloudynights.com/topic/505754-another-real-world-example-of-sonys-star-eater-problem/https://community.sony.com/t5/Alpha-NEX-Cameras/Star-eater-in-bulb-mode/td-p/508740https://www.dpreview.com/forums/post/55719652
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